__path__有什么用? [英] What is __path__ useful for?

问题描述

我从没注意到在今天之前在某些软件包上定义的__path__属性.根据文档:

I had never noticed the __path__ attribute that gets defined on some of my packages before today. According to the documentation:

包支持另一项特殊功能 属性__path__.这是 初始化为包含以下内容的列表 存放目录的名称 软件包前的__init__.py 在该文件中执行.这 变量可以修改；这样做 影响以后对模块的搜索 和包含在 包.

Packages support one more special attribute, __path__. This is initialized to be a list containing the name of the directory holding the package’s __init__.py before the code in that file is executed. This variable can be modified; doing so affects future searches for modules and subpackages contained in the package.

虽然此功能并不常见 需要时，可以用来扩展 包中找到的一组模块.

While this feature is not often needed, it can be used to extend the set of modules found in a package.

有人可以向我解释这到底是什么意思，为什么我要使用它?

Could somebody explain to me what exactly this means and why I would ever want to use it?

推荐答案

这通常与 pkgutil一起使用以便将软件包放在磁盘上.例如，zope.interface和zope.schema是单独的发行版(zope是命名空间包").您可能在/usr/lib/python2.6/site-packages/zope/interface/中安装了zope.interface，而在/home/me/src/myproject/lib/python2.6/site-packages/zope/schema中更本地地使用了zope.schema.

This is usually used with pkgutil to let a package be laid out across the disk. E.g., zope.interface and zope.schema are separate distributions (zope is a "namespace package"). You might have zope.interface installed in /usr/lib/python2.6/site-packages/zope/interface/, while you are using zope.schema more locally in /home/me/src/myproject/lib/python2.6/site-packages/zope/schema.

如果将pkgutil.extend_path(__path__, __name__)放在/usr/lib/python2.6/site-packages/zope/__init__.py中，则zope.interface和zope.schema都是可导入的，因为pkgutil将__path__更改为['/usr/lib/python2.6/site-packages/zope', '/home/me/src/myproject/lib/python2.6/site-packages/zope'].

If you put pkgutil.extend_path(__path__, __name__) in /usr/lib/python2.6/site-packages/zope/__init__.py then both zope.interface and zope.schema will be importable because pkgutil will have change __path__ to ['/usr/lib/python2.6/site-packages/zope', '/home/me/src/myproject/lib/python2.6/site-packages/zope'].

pkg_resources.declare_namespace(Setuptools的一部分)与pkgutil.extend_path类似，但更了解路径上的压缩.

pkg_resources.declare_namespace (part of Setuptools) is like pkgutil.extend_path but is more aware of zips on the path.

手动更改__path__并不常见，也可能没有必要，尽管在调试名称空间包的导入问题时查看变量很有用.

Manually changing __path__ is uncommon and probably not necessary, though it is useful to look at the variable when debugging import problems with namespace packages.

您也可以使用__path__进行猴子补丁，例如，有时我会通过创建文件distutils/__init__.py来创建猴子补丁distutils，而该文件早于sys.path:

You can also use __path__ for monkeypatching, e.g., I have monkeypatched distutils at times by creating a file distutils/__init__.py that is early on sys.path:

import os
stdlib_dir = os.path.dirname(os.__file__)
real_distutils_path = os.path.join(stdlib_dir, 'distutils')
__path__.append(real_distutils_path)
execfile(os.path.join(real_distutils_path, '__init__.py'))
# and then apply some monkeypatching here...

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